HIV evolves rapidly and strains with widely divergent nucleotide sequences have been isolated from a number of geographic locations. Detailed information on the number of distinguishable HIV serotypes circulating within different communities is lacking and, because the mechanisms for inducing protective immunity are unknown, it is not known whether effective AIDS vaccine preparations will need to contain immunogenic material derived from viral variants geographically associated with the target population or with phases of the epidemic. Thus, there is a need to monitor genetic and antigenic variation of HIV in selected geographical locations which, in turn, will allow assessment of the impact of this variation on vaccine efficacy. HIV vaccine efficacy trials are currently being planned that would be carried out at both domestic and international sites. While it may not be possible to tailor the initial vaccines that will be tested in these early trials to the major virus strain present at each site, it will be of considerable interest to identify the major virus genotypes/serotypes/immunotypes present at these sites in order to analyze efficacy of the test vaccines. The NIAID currently supports research aimed at identifying the major genotypes of HIV that exist in the world, including the funding of both a genetic cloning and sequencing laboratory and an HIV sequence database and analysis unit. there is now a need to correlate antigenic properties of the virus with genetic data. The contractor will be provided with specimens by investigators, identified by the Project Officer, who are operating in geographical areas where vaccine trials may potentially occur. It is hoped that data resulting from this contract will permit informed decisions regarding virus type(s) to which vaccines should be modeled and will aid in the assessment of vaccine efficacy at those sites.